Surface acoustic wave (SAW) devices use surface waves propagated on the surface of an elastic solid for electronic signal processing. SAW devices are typically implemented on a piezoelectric substrate using transducers with metal film interdigital fingers which generate and detect acoustic waves. Within this document, the term "acoustic element" is used to define that portion of the geometry of a SAW structure that interacts with, detects, or generates, acoustic waves within an acoustically active region of the SAW structure. For example, within a transducer, the acoustic elements are the interdigitated fingers within the acoustic track. In the case of a reflector, the acoustic elements are the conductive strips within the reflector. The geometry of the acoustic elements on the piezoelectric substrate plays a significant role in the signal processing and frequency response characteristics of a SAW device.
In addition to the SAW geometry, design parameters in a SAW device design include the acoustic attenuation and reflection coefficient of acoustic elements on the SAW structure, which in turn help determine the acoustic bandwidth and loss of a particular SAW device component. For example, a transducer having a low reflection coefficient per finger typically has a narrow acoustic bandwidth and a low loss. The reverse is true such that a transducer with a high reflection coefficient usually has a wide acoustic bandwidth and high loss. Oftentimes, it is desirable to have a SAW device component with low loss while providing a wide acoustic bandwidth. However, because of prior art manufacturing techniques, a tradeoff is made between the acoustic bandwidth and the loss depending on the intended use of the SAW device. These tradeoffs can result in more complex product designs requiring circuits having a low loss and high frequency response bandwidth.
There is a need to provide a SAW device that has a low loss and a wide acoustic bandwidth. Such devices are not generally found in the prior art because of the tradeoff which must be made between acoustic attenuation and reflection coefficient of acoustic elements within the SAW device. However, such tradeoffs can result in product design complexity. For example, in a filter application, multiple SAW devices may have to be combined to satisfy the needs of low loss and wide acoustic bandwidth. Therefore, an improved design approach is needed for surface acoustic wave devices.